1. Field of the Invention
The present invention relates to intermediate frequency (IF) transceivers used to process analog signals converted to IF frequencies, and more specifically to receive path implementations for IF transceivers.
2. Description of Related Art
Intermediate frequency (IF) transceivers are used in a variety of applications to process IF signals converted from different frequency electro-magnetic transmissions. IF transceivers may be implemented as CMOS integrated circuits (ICs) with on-chip signal processing. One application for an IF transceiver is in a small size radio for a consumer NPCS service. In this application, the IF transceiver has receive section circuitry, which converts IF analog signals to digital baseband I and Q data, and transmit section circuitry, which converts digital baseband I and Q data to IF analog signals. The digital baseband I and Q data may also be provided to other ICs in the NPCS radio.
The receive section circuitry of IF transceivers converts analog IF input signals to digital complex baseband signals. Prior receive path implementations for IF transceivers have suffered from numerous problems. Signal distortion occurs if the input fixed-gain amplifier does not have matched impedance. Output integrity and data conversion accuracy is lost if the AGC amplifier introduces varying phase shift into the signal path at different gain levels. Sample accuracy is degraded if the sampling circuitry does not operate on jitter-free clock edges, and power requirements are increased if the sample circuitry works on a clock period having a low percentage duty cycle. Design and circuit complexity is increased if the complex filter in the delta-sigma ADC is not made to efficiently handle quantization noise shaping. The performance of the receive path implementation is degraded if the design specifications are not chosen to provide good anti-aliasing properties.